Now that I'm pregnant, do I have to stop drinking coffee and avoid other sources of caffeine?

There's general agreement that pregnant women and those trying to conceive should avoid consuming large quantities of caffeine. But after decades of controversy and conflicting evidence, there's still no consensus on how much caffeine is safe during pregnancy.

To err on the side of caution, the March of Dimes advises women to limit their caffeine intake to less than 200 milligrams per day, which is about one 12-ounce cup of coffee. (See the chart below to get a sense of the amount of caffeine in common beverages and foods.)

What are the concerns about caffeine consumption during pregnancy?

A highly publicized 2008 study found that women who consumed 200 mg or more of caffeine a day had double the risk of miscarriage of those who took in no caffeine. However, not all studies show a link between caffeine consumption and a higher risk of miscarriage.

A study in Denmark found that the risk of stillbirth more than doubled in women who drank eight cups of coffee or more each day compared with women who didn't drink coffee.

Other research has shown that newborns whose mother consumed more than 500 mg of caffeine a day had faster heart rates and breathing rates and spent more time awake in the first few days after birth.

Some studies show an association between high caffeine consumption and a slight reduction in the baby's birth weight, but other research has shown no link. There does not appear to be an association between moderate caffeine consumption and preterm birth. And caffeine consumption does not appear to increase the risk of gestational hypertension or preeclampsia.

One thing's for sure: You'll feel better if you don't consume a lot of caffeine. It's a stimulant, so it raises your heart rate. Plus, it can make you feel jittery and cause insomnia. Caffeine can also contribute to heartburn by stimulating the secretion of stomach acid.

These effects may be more pronounced as your pregnancy progresses. That's because your body's ability to break down caffeine slows, so you end up with a higher level of it in your bloodstream. During the second trimester, it takes almost twice as long to clear caffeine from your body as when you're not pregnant. During the third trimester, it takes nearly three times as long.

This can affect the amount of caffeine that crosses the placenta and reaches your baby, who can't process it efficiently. (This is true for newborn babies as well, which is why it's also a good idea to limit caffeine if you're breastfeeding, especially for the first few months.)

Finally, there's one more reason to cut back on coffee and tea, whether it's caffeinated or not. These beverages contain compounds called phenols that make it harder for your body to absorb iron. This is particularly important because many pregnant women are already low on iron. If you have coffee or tea, drink it between meals so it'll have less of an effect on your iron absorption.

Which foods and beverages contain caffeine?

Coffee is one, of course. The amount of caffeine in a serving of coffee varies widely, depending on the type of bean, how it's roasted, how it's brewed – and, obviously, on the size of the coffee cup. (Although espresso contains more caffeine per ounce, it's served in a tiny cup, so a full cup of brewed coffee will deliver more caffeine.)

To manage your caffeine intake, though, you'll need to be aware of other sources, like tea, soft drinks, energy drinks, chocolate, and coffee ice cream. Caffeine also shows up in herbal products and over-the-counter drugs, including some headache, cold, and allergy remedies. Read labels carefully.

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